On iOS, sometimes I can add a reaction when double-tapping and holding, but often times, especially if the message contains a link, that double-tap and hold is executed in the middle of the cell, and if that's the link, Safari gets opened instead. The only way to solve this is via AccessibilityCustomActions, which give the developer control over anything that can be performed on a cell. That's the VoiceOver equivalent of swiping left or right, or tpping on individual portions of a message. Some apps, like Twitter, also put links in there for simplicity instead of trying to rely on the links rotor.
If you work well with a sample app to make adding this easier, here's a good article with sample code by Apple that explains, among other things, adding custom actions to an app.